The present invention relates generally to electronic control systems for air conditioners, heat pumps and refrigeration equipment. More particularly, the invention relates to an apparatus and method using digital circuitry for controlling the flow of refrigerant through the refrigeration system to optimize efficiency and extend component life.
Air conditioning systems, heat pump systems and refrigeration equipment use a considerable amount of electrical energy. Every year more and more owners of residential and commercial buildings will add central air conditioning and heat pump systems. As demand for energy climbs and as energy becomes more costly, it is expected there will be a considerable emphasis placed on improving the efficiency of the refrigeration cycle.
One area which appears promising is to improve the manner in which refrigerant is metered through the system. The refrigerant cools by evaporation in a heat exchanger commonly called an evaporator coil. The refrigerant is metered to the evaporator coil through an orifice sometimes called an expansion valve. Ideally a refrigeration system should meter just enough refrigerant into the evaporation coil, so that the refrigerant extracts heat throughout the entire length of the coil as it evaporates. Due to the changing dynamics of the system, changes in thermostat setting, changes in load from sun, wind and so forth, the optimal performance is not always easy to achieve.
For example, when the temperature surrounding the evaporator coil is high, refrigerant is rapidly converted from the liquid phase to the gaseous phase and there may not be enough refrigerant in the liquid phase to fill the entire evaporator coil. When this occurs, efficiency suffers, since, in effect, some of the evaporator coil is being wasted. On the other hand, if the temperature surrounding the evaporator coil is low, there may not be enough heat present to cause all of the refrigerant to evaporate from the liquid phase to the gaseous phase When this occurs, liquid refrigerant may enter the compressor, degrading efficiency and possibly damaging the compressor. Conventional refrigeration systems have employed a number of different control schemes for metering the refrigerant into the evaporator coil. Although purportedly successful to some degree, there still remains a great deal of room for improvement.
The present invention addresses this problem through the use of a microprocessor-based control system and digitally controlled valve. Precise metering of refrigerant is made possible by a decoupled sensing arrangement which is virtually immune from previously troublesome errors caused by changing system dynamics. The system is able to maintain efficient operation at low temperature levels not heretofore readily attained.
The result is a state-of-the-art air conditioning or heat pump system which offers high efficiency and greater comfort. Because the flow of refrigerant is controlled accurately, the likelihood of introducing liquid-phase refrigerant into the compressor is greatly reduced. This results in longer compressor life.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.